1. Field of the Invention
The present invention generally relates to a light source module and an optical element thereof and, in particular, to a backlight module and a light guide unit thereof.
2. Description of Related Art
FIG. 1 is a schematic cross-sectional view of a conventional backlight module. Referring to FIG. 1, a conventional backlight module 100 includes a light guide plate 110, a cold cathode fluorescent lamp (CCFL) 120, a reflecting plate 130, and a diffusion plate 140. The light guide plate 110 has a first surface 112, a second surface 114 opposite to the first surface 112, and a light incident surface 116 connecting the first surface 112 and the second surface 114. The CCFL 120 is disposed beside the light incident surface 116 and is adapted to emit a light beam 122 towards the light incident surface 116. A portion of the light beam 122a enters the light guide plate 110 through the light incident surface 116 and is transmitted to the reflecting plate 130 through a light diffusion effect of titanium dioxide (TiO2) net points 114a on the second surface 114. The reflecting plate 130 reflects a portion of the light beam 122a and enables the portion of the light beam 122a to pass through the second surface 114, the first surface 112, and the diffusion plate 140 in sequence. On the other hand, after entering the light guide plate 110, a portion of light beam 122b is transmitted to the first surface 112 through the light diffusion effect of the TiO2 net points 114a. Next, the portion of the light beam 122b passes through the first surface 112 and the diffusion plate 140 in sequence. After passing through the diffusion plate 140, the light beam 112 (including the portion of the light beam 112a and the portion of the light beam 112b) forms a surface light source.
When the TiO2 net points 114a are formed on the second surface 114 in a screen printing manner, sizes and pitches of the TiO2 net points 114a may not be quite small. Therefore, when no diffusion plate 140 is disposed above the light guide plate 110, discontinuous bright spots formed by the TiO2 net points 114a may be recognized by naked eyes, such that the backlight module 100 may not form a uniform surface light source.
In order to improve the problem that the discontinuous bright spots are recognized by the naked eyes, in the prior art, the discontinuous bright spots are made to be fuzzy by the diffusion plate 140 for achieving a shielding effect. However, the additionally used diffusion plate 140 causes an increased cost and an optical loss.